1. Field of the Invention
The invention relates to a method for manufacturing a capacitor in a semiconductor device and the capacitor.
2. Description of the Related Art
Recently, the need for memory elements has increased with developments of techniques for manufacturing semiconductor devices. In a semiconductor device, a capacitor is used as a means for storing data. The capacitance of such a capacitor depends on the electrode area and the dielectric constant of a dielectric film interposed between electrodes of the capacitor.
However, as semiconductor devices become more highly integrated, the capacitor area given in the semiconductor device is reduced. Accordingly, the electrode area of the capacitor decreases, thereby causing a reduction in the capacitance of the capacitor.
In order to solve this problem, a capacitor comprising a TaON thin film of a high dielectric constant has been proposed, in which the TaON film has a metal film-insulating film-silicon (MIS) structure. An upper electrode over the TaON thin film is formed using a laminated structure composed of a polysilicon film deposited on a TiN film in order to enhance interface characteristics.
FIG. 1 is a cross-sectional view illustrating a conventional method for manufacturing a capacitor with a TaON thin film in a semiconductor device. As shown in FIG. 1, according to the conventional capacitor manufacturing method, a TaON thin film 2 having a high dielectric constant is deposited over a lower electrode 1, for example, a polysilicon film.
Then, a TiN/polysilicon film 3 having a laminated structure is deposited over the TaON thin film 2. The deposition of the TiN/polysilicon film 3 is achieved by forming a TiN thin film in a CVD (Chemical vapor Deposition) chamber using TiCl4 as a precursor and NH3 as a reaction gas. Thus, a capacitor with an MIS structure is completely formed.
However, there are some problems involved in the conventional method for manufacturing such a capacitor of a semiconductor memory device.
For example, as semiconductor devices become more highly integrated, the cell size is reduced, even though the capacitance per cell requisite for stably driving the device does not vary. Therefore, the TaON thin film having a single layer structure cannot assure a high enough capacitance of the capacitor and suppression of leakage current at the same time.
Also, after the deposition of the TaON thin film as a dielectric film and before the formation of the polysilicon film as an upper electrode, the formation of a TiN thin film has to be carried out in the CVD chamber using TiCl4 as a precursor and NH3 as a reaction gas in order to enhance the interface characteristics of the TaON thin film and the polysilicon film. Accordingly, there is an increase in the manufacturing costs for the additional process.
Therefore, the present invention has been made in order to solve the above-mentioned problems in the related art. An object of the present invention is to provide a capacitor and a method for manufacturing a capacitor in a semiconductor device, which is capable of achieving an improvement in the interface characteristics while assuring a high capacitance and a low leakage current.
In accordance with one aspect, the present invention provides a method for manufacturing a capacitor in a semiconductor device, comprising: forming a nitride film over a lower electrode, which is on a semiconductor substrate; forming a TaON film over the nitride film; forming an Al2O3 film over the TaON film; and forming an upper electrode over the Al2O3 film.
In accordance with another aspect, the present invention provides a method for manufacturing a capacitor in a semiconductor device, comprising: forming a nitride film over the lower electrode, which is on a semiconductor substrate, by using plasma; forming an amorphous TaON thin film over the nitride film; subjecting the amorphous TaON thin film to an RTA (Rapid Thermal annealing) treatment; forming an Al2O3 film over the amorphous TaON thin film; subjecting the Al2O3 film to a furnace vacuum thermal treatment; and forming a polysilicon film over the Al2O3 film to form an upper electrode.
In accordance with yet another aspect, the present invention provides a capacitor comprising: a lower electrode; a nitride film formed on the lower electrode; a TaON film formed over the nitride film; an Al2O3 film formed over the TaON film; and an upper electrode formed on the Al2O3 film film.